You're right in that it's all about comfort level. My preferred mode of walking around with my rig is to have the camera in some sort of bag and only pull it out when I need it. That obviously wouldn't work for you because you need to be ready to grab a shot of a bird at a second's notice. But my targets are different and I don't feel right having the camera around my neck, especially in a city environment. In fact, neither of my bodies has a neck strap. They both have wrist straps. So for me, ease of movement in and out of a bag is important. And again, as stated above, I tend to shoot at closer range, but not always "indoor" close. When I shoot street shots, I like to be at "standoff range" so the subjects of my shots don't notice me. There again, a less inconspicuous lens helps.

That said, I've been questioning the need for my current collection of smaller primes and have started thinking about downsizing my collection. I've been reading David duChemin lately and he suggests working with one lens exclusively for a week or so to really get to know the characteristics of the lens. I'm thinking this would also be a good way to determine the utility of the lens. Do I really need a 35mm f2 when my default lens (24-105) will do 35mm at f4? I do like my 85mm f1.8 and I tend to choose that over the 50mm f1.4 unless I really need the shorter FL. Note that speed is not a consideration there. So the 50mm f1.4 could go as well. If I also sell the T1i with the kit lens and the 55-250, plus some extra stuff that only works with the T1i, I could easily afford a 135mm F2L and have funds left over to put towards a FF down the road. That would give me 10-22, 24-105, 135, and if I really want to travel light, the 85. Add a 1.4x TC and I'd have some long range if/when I need it.

Starting this weekend I'm going to use one prime per week exclusively (unless something out of the ordinary requires otherwise). It'll be interesting to see if I can come up with images from a given prime that I could not have produced with the 24-105.

the fastness of the lens is just a luxury.I don't really understand why a wide angle needs to go that wide. If you're putting on a wide angle and taking a picture of a person, you need to be far away anyhow, and if you open the aperture right up, everything is pretty much going to be in focus anyhow unless it's a mountain in the distance or something.

Now on the other hand, saying you don't need fast lenses when you have a 500mm with an F4. Sorry, but that's fast for a lens that size. It's fast enough to give you fairly razor thing DOF at distance. That would probably compare to about a 100mm at 2.8 or something as far as the DOF goes. And in this case, you shelled out just to get that extra "fastness" in that lens.

I don't shoot pictures wide open all that often, but it's nice to have that flexibility to play. Hell, most of the time, I think a lot of my lenses will be set to about 4.5-8. But what's interesting about that is because the fast lesnses are so big, they get a bigger piece of glass, so when you do stop it down, you end up with less distortion and less gooey edges, so having the fast lens (maybe not using the speed) still has advantages over a similar but slower lens that you are forced to use at wide open, producing the not so pretty, but gooey edges.

for example, people who own and know their way around the 24-70mm F2.8 quite often avoid shooting less then 3.5 on it because of they outter edges when that lens is shot wide open. But people love that lens because it is super sharp when used correctly. And for the occasional use, it can do some fun things at 2.8 when playing about if needed.

So no, we don't need the speed (some people are excessively in love with it and only shoot wide open) but it's there for more reason then just being wide open when looking at the big picture.

You're right in that it's all about comfort level. My preferred mode of walking around with my rig is to have the camera in some sort of bag and only pull it out when I need it. That obviously wouldn't work for you because you need to be ready to grab a shot of a bird at a second's notice. But my targets are different and I don't feel right having the camera around my neck, especially in a city environment. In fact, neither of my bodies has a neck strap. They both have wrist straps. So for me, ease of movement in and out of a bag is important. And again, as stated above, I tend to shoot at closer range, but not always "indoor" close. When I shoot street shots, I like to be at "standoff range" so the subjects of my shots don't notice me. There again, a less inconspicuous lens helps.

That said, I've been questioning the need for my current collection of smaller primes and have started thinking about downsizing my collection. I've been reading David duChemin lately and he suggests working with one lens exclusively for a week or so to really get to know the characteristics of the lens. I'm thinking this would also be a good way to determine the utility of the lens. Do I really need a 35mm f2 when my default lens (24-105) will do 35mm at f4? I do like my 85mm f1.8 and I tend to choose that over the 50mm f1.4 unless I really need the shorter FL. Note that speed is not a consideration there. So the 50mm f1.4 could go as well. If I also sell the T1i with the kit lens and the 55-250, plus some extra stuff that only works with the T1i, I could easily afford a 135mm F2L and have funds left over to put towards a FF down the road. That would give me 10-22, 24-105, 135, and if I really want to travel light, the 85. Add a 1.4x TC and I'd have some long range if/when I need it.

Starting this weekend I'm going to use one prime per week exclusively (unless something out of the ordinary requires otherwise). It'll be interesting to see if I can come up with images from a given prime that I could not have produced with the 24-105.

by the sounds of things, you money would be better spend on a different lens then a 70-200mm F4. It is a fantastic lens, one of the best I've owned. But in day to day uses, there really isn't a need for that kind of reach on a crop body unless you're out looking for wildlife (or maybe throwing an extension tube on)

My concern for you with the 135 on the other hand is that you need to be 6-8' away from any subject before the lens can start autofocusing, this can be inconvenient, but it does solve your long range problem. It is quite light, and it's all black, so it definitely flys under the radar a lot more then the other light coloured telephotos. The only thing I find odd about it is the massive hood it has. It makes a nicely sized lens huge. I'll often use my hand to sheild light as a result if I'm finding the hood imposing.

Good luck with the choice. But it sounds like most of your work will be done in the "normal" range of use. Telephotos are fun, but they stay at home a lot when you're not expecting to run into wildlife on a regular basis. But when you're off somewhere that you know you'll need it, it becomes your best friend.

Remember that AF is quicker and more accurate on many Canon bodies when the lens is f/2.8 or faster. So lots of fast action shooting benefits from a fast lens, even when the exposure is stopped down.

Also the subject isolation you can get with a fast lens is a special look - maybe a bit overdone for portraits, but I still like it enough to shoot a 135/2 wide open all the time.

Finally, some times you just need all the light you can get. I shoot nightscapes/starscapes at ISO3200 with a 24/1.4II near wide open. I guess if the 5D3 really has a clean ISO 12800 then I could get away with an f/2.8 - but I'll wait for reports before I go trading in all my fast primes...

the fastness of the lens is just a luxury.I don't really understand why a wide angle needs to go that wide. If you're putting on a wide angle and taking a picture of a person, you need to be far away anyhow, and if you open the aperture right up, everything is pretty much going to be in focus anyhow unless it's a mountain in the distance or something. ...

I wouldn't shoot a person, generally, with a wide angle, but many of my buildings and scenics are at 24mm, like below:

I wouldn't shoot a person, generally, with a wide angle, but many of my buildings and scenics are at 24mm, like below:

I'm seriously considering a 16-35mm or an 8-15mm, for certain situations. Interestingly, for multi-shot panos, I'm more likely to use my 70-200mm at 70mm.

Dave

I love my 16-35L it is probably attached to my 5DmkII about 95% of the time. I don't find the distortion to be too extreme at 16, it's definitely an improvement on the distortion that the 17-40mm produces, which I could never get used to. Which is why I exchanged it for the 16-35. Since I picked it up, I generally don't use my 24-70 unless I plan to shoot people, but when I do that, I'm more likely to use my 100mm prime. It just feels more right in the hand. And I don't find myself wondering where the zoom is.

I wish I could comment on the 8-15mm, I really want to try it out some day. It appears to be a very neat lens.

I think people are under the belief that you have to have an extreme aperture to produce bokeh.

With the 70-200mmF4 you may not exactly get bokeh if your subject is standing with their back against the wall that you're trying to get out of focus, but that just means, have them step away from it 2 or 3 feet, and you'll get the bokeh you wanted in the first place.

Now on the other hand, saying you don't need fast lenses when you have a 500mm with an F4. Sorry, but that's fast for a lens that size. It's fast enough to give you fairly razor thing DOF at distance. That would probably compare to about a 100mm at 2.8 or something as far as the DOF goes. And in this case, you shelled out just to get that extra "fastness" in that lens....

At the 500mm focal length the max f-stop becomes a matter of size and weight limits. With today's technology, f/4 is about all most of us can hand hold and, in fact, most people use a tripod for these lenses.

I think that one reason to spring for "fast" lenses in the 100mm to 400mm range is so that you can throw on a 1.4 or 2.0x TC and still AF. People aren't worried about bokeh with those lenses, because it's there easily. If the quality of the bokeh is bad, then that's an issue, but most of those lenses have creamy, smooth bokeh.

I love my 16-35L ... Since I picked it up, I generally don't use my 24-70 unless I plan to shoot people, but when I do that, I'm more likely to use my 100mm prime. It just feels more right in the hand. And I don't find myself wondering where the zoom is.
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Interesting thing to mention. When I shoot with a zoom, I compose in the viewfinder and never worry about where the zoom is. I wonder why some people think of that. When I shot with primes I would think about which focal length to pull out of the bag, but with my current kit, my only thought is "do I need more reach" and if the answer is "no" then I stick with the zoom lens that happens to be mounted and compose in the viewfinder.

I think it's mostly that if I take a shot, then tilt the camera down, then bring it back up and take a shot without thinking, the focal length can change on my 24-70mm. I like to fidget and I often knock the zoom or it slides on it's own between shots. So it's a point for me to pay attention to.

Sadly, I also find that I shoot often at one extreme or the other with a zoom lens. I'll either go wide, or full zoom and not use so much of the in between stuff. Which might be why I like having the 16-35 on my camera. It makes me think and use it's zoom in a more considerate way.

I think it's mostly that if I take a shot, then tilt the camera down, then bring it back up and take a shot without thinking, the focal length can change on my 24-70mm. I like to fidget and I often knock the zoom or it slides on it's own between shots. So it's a point for me to pay attention to.
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You've got zoom drift. None of my zooms do that, thank goodness. I saw a band that you put around your lens to combat drift, but I forget where I saw it. It seemed like a simple solution to what, I'd guess, would be an aggravating problem.